In the oil field industry, the need to sever tubular members at points inaccessible from the outside of the members often arises. Generally, such tubular members have irregular inner diameters caused by portions with smaller effective internal diameters than other portions thereof, such as constrictions caused by connectors that connect sections of the tubular members together.
For example, when oil and gas wells, and oil well platforms in ocean locations, become inactive or have reached their designed lifespan, they must be shut down. To form platform pilings in a body of water, tubular members are commonly utilized that extend from the floor of the water body to above the surface of the water body. The elongated tubular members have been assembled with pipe sections connected by special load-bearing connectors, which form internal constrictions.
Well platforms must be removed near or below a mud-line of the water body floor to eliminate navigational hazards. The explosives used to sever the legs of the platform must be internal to the tubular member to obtain the desired depth of cut. Generally, a rigid inner-diameter cutter was used to sever a tubular member. But such cutters have been ineffective to sever the legs due to internal constrictions such as stabbing guides and connectors.
There have been two primary removal or severing methodscbulk explosive and linear-shaped charge. Linear shaped charges are comprised of elongated masses of explosive material having V-shaped cross-sections, and are particularly well suited for such applications because of the great level of control afforded these explosives. Upon detonation of such linear-shaped charges, the V-shape of the explosive material generates a substantially unidirectional explosive jet or vector capable of deep penetration in steel targets/structures. However, an air space is required between the linear-shaped charge and the target to be severed to allow the explosive jet to travel a distance substantially unfettered before meeting incompressible liquids or other obstructions to achieve proper penetration of the target. The air space distance required to achieve proper penetration of the target is known in the art as the "stand-off" distance.
Also, linear-shaped charges were preferred because a minimal amount of explosive compounds were needed to sever a tubular member, allowing a well platform to be dismantled in a controlled manner. To sever a tubular member, the linear-shaped charge must be placed adjacent the region to cut. However, to do so, the explosive must first be run or "fished" through the internal constrictions to the target region, also known as the sever region, and be capable of being deployed at the sever region.
Attempts have been made to deploy a charges through internal constrictions and yet be deployed for detonation of linear-shaped charges. For example, U.S. Pat. No. 4,116,130, issued on Sep. 26, 1978, to Christopher et al., discloses a device for severing tubular members with internal constrictions. The device has a pair of identical hinged-together semicircular parts containing linear-shaped charges. To run through constrictions, the semicircular parts are in folded about a hinge and oriented in a vertical position such that the minimum constriction inner diameter is the radius of the semicircular parts. Upon reaching the portion of the tubular member to be severed, the semicircular parts are then rotated and unfolded towards a horizontal position.
Nevertheless, such severing devices have had inconsistent severing results, as well as the physical limitation on the narrowest internal constriction the device can pass through. Inconsistent severing has occurred from the inability to consistently deploy the cutter components into a planar shape, and irregular sever profiles result such as a V-shaped cut or skewed cut. With either of these irregular sever profiles, a substantial portion of the tubular member, known as a tab, remains, or the charge does not otherwise cut completely through the tubular member. In either case, the tubular member effectively remains intact. When the tubular member fails to be severed, then another trip, with the associated labor and materials expense, must be made to sever the tubular member.
Thus, a need exists for a collapsible cutter that can consistently be run through internal constrictions of a tubular member, and that can be consistently deployed to sever the tubular member.